Field of the Invention
The present invention relates to an image forming apparatus.
Description of the Related Art
As a method of correcting an image processing characteristic, in particular, a gradation characteristic in an image forming apparatus, e.g., a color multifunctional peripheral or a color printer, the following method is known.
First, the image forming apparatus is activated. After a warm-up operation is ended, a pattern image is formed on an image bearing member. Then, the pattern image is transferred onto a sheet. Then, the density of the transferred pattern image is read, and an operation of a gamma correction circuit or the like, which is configured to determine image formation conditions, is adjusted based on the read density information. The method described above is known as a method of stabilizing a quality of an image to be formed (image quality).
FIG. 12 is a flow chart for illustrating an example of a control procedure when the gradation characteristic of the image forming apparatus is adjusted.
In FIG. 12, first, a control switch of the image forming apparatus is turned on to activate the apparatus (Step S201). The image forming apparatus forms a pattern image (Step S202). The image forming apparatus reads the pattern image to acquire its density (Step S203). The image forming apparatus stores a laser output level and the acquired density in association with each other in a memory (Step S204). The image forming apparatus generates, based on the information stored in the memory, a conversion condition (gradation correction condition) for converting a signal value of image data in order to set the gradation characteristic of the image forming apparatus to an ideal gradation characteristic (target gradation characteristic) (Step S205). The gradation correction condition corresponds to, for example, a γ lookup table (hereinafter referred to as “γ-LUT”). The gradation characteristic of the image forming apparatus is adjusted based on the content of the γ-LUT. Such a function is generally referred to as “gradation correction”.
Further, in an image forming apparatus described in U.S. Pat. No. 6,418,281, there is described a method of performing the gradation correction without using a sheet.
In this apparatus, during an image forming operation, a pattern image is formed in a non-image region on the image bearing member. Based on the detection result of reflection light from the pattern image, image formation conditions including a γ-LUT and an exposure amount of a laser beam for adjusting the maximum density of the image are adjusted.
However, even if the density of the image can be corrected to a target value after the gradation correction is performed, when there is a large change between before and after the correction, a user may falsely determine that color deviation is occurring, that is, the image quality is not stable. In particular, when the image forming apparatus automatically performs the gradation correction, it is highly possible that the user falsely recognizes that the color has deviated. As a result, there remains a problem in that the gradation correction performed for stabilizing the image quality is negatively recognized as color deviation by the user.
The present invention has a primary object to provide an image forming apparatus capable of suppressing user's false recognition of regarding gradation correction as a color deviation.